Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 25, 2010. The information contained within may not be the most current and accurate depending on when it is accessed.
By Erin Hodgson, Department of Entomology
Throughout the winter I heard several presentations about isopods, a new early-season soybean pest in the Midwest. Isopods are terrestrial crustaceans most closely related to lobsters and crabs. They have many common names, such as woodlice, pillbugs, sowbugs, and roly-polies.
Although isopods have three major body regions (head, thorax and abdomen) like insects, it is very difficult to distinguish the regions because of the armor-like plates on the back. They have two pair of antennae (usually only one pair is obvious), seven pairs of legs and simple eyes (Fig. 1). Immatures look like adults except are smaller in size and proportion. Most isopods are grey or black and some have dark markings on the back. Adults are oval in shape and three-eighths inch long. In general, the back is convex and the underside is flat or concave.
Figure 1. Isopods have become early-season pests in neighboring states.
Isopods are omnivores that scavenge on dead and decaying plant or animal matter. They will also eat live, young plants such as fruit and vegetables. All life stages breathe through gills, so they must live in habitats with high humidity. No-till field crops can be attractive to isopods because they are protected under crop residue. Isopods are most active in the spring, often feeding at night. Isopods are skittish and some species curl up into a ball when disturbed (Fig. 2).
Figure 2. Some isopods curl up when threatened.
Increasing acreage of no-till systems will encourage isopod development because high moisture is needed for survival. Some areas in Kansas and Nebraska have already experienced economically damaging levels of isopods that required replanting in soybean (Figures 3 and 4). When scouting for other early-season soybean pests, look for clipped or missing plants. Isopods can also feed on unifoliates and scrape off leaf tissue. Managing fields for isopods is difficult because seed treatments and foliar insecticides have not proven effective. Heavily infested areas could till every other year to minimize overwintering populations and reduce soil moisture in the spring.
Figure 3. Isopods have the potential to damage emerging soybean, especially in no-till systems. Photo by Brian McCornack, Kansas State University
Figure 4. Typical isopod damage includes clipping the cotyledon at emergence. Photo by Brian McCornack, Kansas State University
Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. She can be contacted by email at email@example.com or phone (515) 294-2847.